1. Field of the Invention
The invention relates to a voltage converting device and a voltage converting method, and more particularly to a switched capacitor voltage converting device and a switched capacitor voltage converting method.
2. Description of the Related Art
A conventional switched capacitor voltage converting device is shown in FIG. 1 to include two switched capacitor voltage converters 11, 12, and a capacitor Cout for stabilization of an output voltage Vout of the switched capacitor voltage converting device. Each of the switched capacitor voltage converters 11, 12 includes four switches M1 to M4 and a capacitor C having first and second terminals. The stabilization capacitor Cout has a first terminal coupled to the switched capacitor voltage converters 11, 12, and a grounded second terminal.
The switch M1 has a first terminal to receive an input voltage Vin, and a second terminal coupled to the first terminal of the capacitor C.
The switch M2 has a first terminal that outputs the output voltage Vout and that is coupled, to the first terminal of the stabilization capacitor Cout, and a second terminal coupled to the first terminal of the capacitor C.
The switch M3 has a grounded first terminal and a second terminal coupled to the second terminal of the capacitor C.
The switch M4 has a first terminal to receive the input voltage Vin, and a second terminal coupled to the second terminal of the capacitor C.
In this case, the switches M1, M2 and M4 of each of the switched capacitor voltage converters 11, 12 are P-type MOSFETS, and the switch M3 of each of the switched capacitor voltage converters 11, 12 is an N-type MOSFET.
FIG. 2 shows a timing diagram for controlling the switches of the switched capacitor voltage converting device, wherein signals PH1 and PH1B are complementary, and signals PH2 and PH2B are complementary. The switch M1 of the switched capacitor voltage converter 11, and the switches M2, M4 of the switched capacitor voltage converter 12 are controlled using the signal PH1B. The switches M2, M4 of the switched capacitor voltage converter 11, and the switch M1 of the switched capacitor voltage converter 12 are controlled, using the signal PH2B. The switch M3 of the switched capacitor voltage converter 11 is controlled using the signal PH1. The switch M3 of the switched capacitor voltage converter 12 is controlled using the signal PH2.
Each of the switched capacitor voltage converters 11, 12 is switched among a charging state in which the switches M1 and M3 are closed and the switches M2 and M4 are open, a floating state in which all of the switches M1 to M4 are open, and an output state in which the switches M1 and M3 are open and the switches M2 and M4 are closed. In the charging state, the capacitor C is charged to the voltage Vin. In the output state, the capacitor C outputs the output voltage Vout that is equal to 2Vin.
The conventional switched capacitor voltage converting device operates periodically in four sequential durations as follows.
In a first operating duration, the switched capacitor voltage converter 11 operates in the charging state and the switched capacitor voltage converter 12 operates in the output state.
In a first transition duration, both of the switched capacitor voltage converters 11, 12 operate in the floating state.
In a second operating duration, the switched capacitor voltage converter 11 operates in the output state and the switched capacitor voltage converter 12 operates in the charging state.
In a second transition duration, both of the switched capacitor voltage converters 11, 12 operate in the floating state.
In the first and second transition durations, since both of the switched capacitor voltage converters 11, 12 operate in the floating state, the output voltage Vout must be stabilized using the stabilization capacitor Cout for preventing voltage drift.
Accordingly, the conventional switched capacitor voltage converting device uses two switched capacitor voltage converters and a stabilization capacitor to output a stable output voltage. When N output voltages are required, the conventional switched capacitor voltage converting device may use 2N switched capacitor voltage converters that include 2N capacitors C and N stabilization capacitors Cout. The large number of capacitors may result in high cost regardless of whether external capacitor components or capacitors integrated into circuits (large circuit area may be required) are used.